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arXiv 1209.3013astro-ph.CO
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论星系恒星形成效率的缺乏演化

On the Lack of Evolution in Galaxy Star Formation Efficiency

Peter S. Behroozi, Risa H. Wechsler, Charlie Conroy

摘要:

利用重建的星系恒星形成历史,我们计算了星系恒星形成的瞬时效率(即,恒星形成率除以重子吸积率)从$z=8$到现在。这种效率在特征晕质量10^11.7兆太阳附近表现出一个明显的峰值,这与长期以来对吸积气体维里激波加热质量尺度的理论预测相吻合。在特征晕质量以上,效率随着质量的负三分之四次方而下降;在特征质量以下,效率随着质量的平均三分之二次方而下降。相比之下,效率的形状和归一化自z=4以来变化很小。我们表明,时间无关的恒星形成效率简单地解释了宇宙恒星形成率的形状,因为z=4的暗物质吸积率。从早期到z=2的宇宙恒星形成的增加对星系形成效率特别敏感。效率的质量依赖性强烈地限制了大多数恒星形成的发生,结果是三分之二的恒星形成发生在特征质量的三倍范围内的晕内,这个范围包括银河系的质量。

英文摘要:

Using reconstructed galaxy star formation histories, we calculate the instantaneous efficiency of galaxy star formation (i.e., the star formation rate divided by the baryon accretion rate) from $z=8$ to the present day. This efficiency exhibits a clear peak near a characteristic halo mass of 10^11.7 Msun, which coincides with longstanding theoretical predictions for the mass scale relevant to virial shock heating of accreted gas. Above the characteristic halo mass, the efficiency falls off as the mass to the minus four-thirds power; below the characteristic mass, the efficiency falls off at an average scaling of mass to the two-thirds power. By comparison, the shape and normalization of the efficiency change very little since z=4. We show that a time-independent star formation efficiency simply explains the shape of the cosmic star formation rate since z=4 in terms of dark matter accretion rates. The rise in the cosmic star formation from early times until z=2 is especially sensitive to galaxy formation efficiency. The mass dependence of the efficiency strongly limits where most star formation occurs, with the result that two-thirds of all star formation has occurred inside halos within a factor of three of the characteristic mass, a range that includes the mass of the Milky Way.

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